118 DR. E. KLEIN. 



blastoderm, but develop, according to Kupfer, after the type 

 of "free-cell formation,^' probably (p. 218) out of a fluid or 

 semifluid blastema, comparable to that of insects (Musca, 

 Chironomus) ; this blastema is situated in the periphery of the 

 yolk, and in it appear at first nuclei — larger than those of the 

 embryo-cells of the segmented blastoderm — around which the 

 substance of that blastema gradually accumulates as " cell- 

 substance." 



Kupfer believes (p. 220) that this blastema is not only 

 limited to that part where it was seen by him (Kupfer 

 did not examine sections, but observed only fresh ova in 

 surface and profile views), i. e. at the periphery around the 

 blastoderm, but that it extends over the whole surface of the 

 ovum, and is concealed by the blastoderm which gradually 

 spreads (grows) over it. Thus Kupfer maintains that, 

 independently of the blastoderm, a layer of cells appears 

 which covers the yolk. Kupfer is unable to say whether 

 this layer has anything to do with the formation of the hypo- 

 blast (" feuillet muqueux " of Lereboullet) or not. 



Van Bambeke,^ in examining vertical sections through the 

 meridian of the ovum of osseous fish at the end of segmen- 

 tation, finds (1. c, p. 1057) : " la calotte blastodermique 

 se compose de deux parties parfaitement distinctes, une 

 superieure, representee par les cellules issues du fractionne- 

 ment du disque, et qui entourent la cavite de segmentation 



; Pautre partie de la calotte blastodermique est formee 



par une couche .... qui ne prend point part au fractionne- 

 ment." On account of this latter portion being situated 

 between the segmented blastoderm and the yolk, Bambeke calls 

 it "couche intermediaire," and distinguishes in this " couche 

 intermediaire" a peripheral thick portion (bourrelet p^riphe- 

 rique) from a central thin part (1. c, p. 1058) ; the former pos- 

 sesses in vertical section a triangular shape, and is therefore 

 to be regarded as a prism bent into an annular mass and resting 

 •with one surface on the upper segment of the yolk-sphere ; 

 its external surface, i. e. that directed outwards, is free, and 

 the upper surface supports the peripheral part of the seg- 

 mented germ. 



The central portion of the " couche interm^diaire " is a 

 very thin lamella uniting the inner angle of the prismatic 

 ring, and thus separating the segmented germ from the yolk. 



Bambeke thinks that this latter, i. e. the central thin 

 lamella, has probably grown from the periphery, as it is not 

 present in earlier stages ; it forms later on the hypoblast or 

 " feuillet muqueux " of the blastoderma, and accompanies 

 this latter while growing around the yolk. 



